PILE FOUNDATION – NEED AND FUNCTIONS

Pile foundation is required when the soil bearing capacity is not sufficient for the structure to withstand. This is due to the soil condition or the order of bottom layers, type of loads on foundations, conditions at site and operational conditions.

Many factors prevent the selection of surface foundation as a suitable foundation such as the nature of soil and intensity of loads, we use the piles when the soil have low bearing capacity or in building in water like bridges and dams

A pile foundation consists of two components: Pile cap and single or group of piles. Piles transfers the loads from structures to the hard strata, rocks or soil with high bearing capacity. These are long and slender members whose length can be more than 15m.

Piles can be made from concrete, wood or steel depending on the requirements. These piles are then driven, drilled or jacked into the ground and connected to pile caps. Pile foundation are classified based on material of pile construction, type of soil, and load transmitting characteristic of piles.

The use of pile foundations as load carrying and load transferring systems has been for many years. Timber piles were used in early days, driven in to the ground by hand or holes were dug and filled with sand and stones. The use of steel pile started since 19th century and concrete piles since 20th century.

With the change in technology and industrial revolution, many advance systems have been devloped for pile driving from the invention of steam and diesel pile driving machines.

The use of pile foundations is increasing day by day due to non-availability of land for construction. Heavy multi-storyed building are being constructed, and load from these structures can not be directly transferred to ground due to low bearing capacity issue and stability issues of building during lateral load application. So, demand for use of pile foundations are increasing day by day. Due to this demand for piles, there have been many improvements in piles and pile driving technology and systems. Today there are many advanced techniques of pile installation.

Function of Pile Foundation:

As other types of foundations, the purpose of pile foundations is:

– To transmit the buildings loads to the foundations and the ground soil layers whether these loads vertical or inclined

– To install loose cohesion less soil through displacement and vibration.

– To control the settlements; which can be accompanied by surface foundations.

– To increase the factor of safety for heavy loads buildings

The selection of type of pile foundation is based on site investigation report. Site investigation report suggests the need of pile foundation, type of pile foundation to be used, depth of pile foundation to be provided. The cost analysis of various options for use of pile foundation should be carried out before selection of pile foundation types.

Unless the ground condition is rocks, for heavy construction and multi-storied buildings, the bearing capacity of soil at shallow depth may not be satisfactory for the loads on the foundation. In such cases, pile foundation has to be provided. The number of piles in a pile groups required is calculate from the pile capacity of single pile and the loads on the foundation. Piles are a convenient method of foundation for works over water, such as jetties or bridge piers.

Generally in sandy soils, black cotton soils and in water logging soils we use piles, in many cases we use friction piles rather than end bearing piles. Again in piles there are precast piles and cast insitu piles.